It is known that there are two general types of rear truck doors: a) side-opening doors and b) doors of overhead type.
In both cases, manufacturers always want to have the tallest opening possible to ease and optimize the loading of the vehicle (ex. truck, van, etc.).
For a side-opening door, there are no limitation constraints as to the upper section. In contrast, for doors of overhead type, the counterbalancing system is always on the top of the door which reduces the usable opening space for the vehicle. For this reason, manufacturers try to have counterbalancing systems which take up the least amount of headroom, etc.
It is also known that in North American markets, there are mainly two types of counterbalancing systems that are used with such overhead doors.
The first type is with a “live” axle. Typically, a cable links together the bottom of the door to a drum. This drum is fixed to a corresponding rotating shaft (i.e. “live” axle) of the counterbalancing system. Counterbalancing is usually made with a spring-plug assembly including a stationary plug fixed to an anchor plate, a winding plug fixed to the shaft, and a torsion spring that links the two plugs together.
The second type of counterbalancing systems is with a “dead” axle shaft. In this case, a “drum-plug” is free to move and rotate on the counterbalancing shaft. Typically, a cable links together the bottom of the door to the drum-plug. On the other side, a winding plug is fixed to the shaft. The counterbalancing system links the winding plug to the drum-plug via the spring.
Taking now a closer look at counterbalancing systems of the second type, that is, “dead axle shaft” systems, particularly in the case of truck doors provided with such a dead axle shaft counterbalancing system, it is also known that the round tubular shaft is normally held in place with three brackets fixed to the frame of the truck door.
Typically, manufacturers provide a square shape onto the tubular shaft which fits into a corresponding square hole in one of these three brackets, namely the central bracket, to block the rotation of the tubular shaft. These types of brackets are as small as possible to reduce the headroom of the counterbalancing system.
Currently, such a conventional counterbalancing system is put under tension by applying turns to the winding plug through the winding hole and then fixing the winding plug to the shaft using set screws. Given that space available within the vehicle (ex. truck) to add turn(s) to the winding plug is limited to about 90 degrees, the winding plug normally has 4 or 6 winding holes, and 2 or 3 set screws.
Industry typically uses oil tempered springs to counterbalance the weight of the door. This kind of spring relaxes over time which reduces the counterbalancing torque it is able to provide, and makes the door become “off-balanced” (i.e. not properly counterbalanced, etc.).
Manufacturers and/or users of these counterbalancing systems need to re-adjust the spring tension occasionally to keep an optimal weight counterbalance for the door.
Another drawback associated with these conventional counterbalancing systems is that because of the limited space within the vehicle, adding turns to the counterbalancing system is a difficult operation. Also, in some cases, set screws and winding holes are not easily accessible.
Furthermore, before releasing tension on a given winding hole, the tension of the spring needs to be completely secured by a second hole. Therefore, at least 2 holes need to be accessible at the same time. If the tension is not properly secured, the system will unwind which might be undesirable for installer and/or cause damage to the spring.
Another drawback associated with these conventional counterbalancing systems is that tightening of the screws often deforms the tubular shaft. When re-adjusting the tension of the spring, the screw needs to be un-tightened and then re-tightened again, in a close range, which weakens the tubular shaft and makes the re-adjustment even more difficult since the shaft progressively becomes oval-shaped.
The Assignee of the present application has developed various new products and manufacturing processes over the years, particularly in relation to cones, plugs, counterbalancing systems and the like, for which various US utility patents and design patents have been obtained (see some examples listed below), the contents of which are incorporated herein by reference: U.S. Pat. Nos. 6,174,575; 6,279,268; 6,378,170; 6,485,006; 6,502,281; 6,681,809; 6,694,673; 6,712,116; 6,907,964; 6,931,810; 6,959,751; 6,986,378; 6,988,527; 7,000,292; 7,000,354; 7,086,441; 7,350,333; 7,441,749; 7,543,625; 7,600,344; D490,685; D520,338; and D524,633.
The Assignee of the present application has also filed various other US patent applications having become public, the contents of which are also incorporated herein by reference: 2002/0117787 A1; 2004/0000109 A1; 2004/0020609 A1; 2005/0006545 A1; 2007/0012410 A1; 2007/0084012 A1; 2007/0204515 A1; 2007/0283525 A1; 2009/0314869 A1; and 2011/0240236 A1.
Nonetheless, despite all of these innovations, there is always a need to continue improving and find better and/or different ways of winding (ex. tensioning, etc.) a counterbalancing system such as the ones used in trucks, vans and the like.